Explosion proof enclosures are commonly used in hazardous locations in order to contain explosions that may occur within the enclosure and prevent sparks occurring within the enclosure from igniting vapors, gases, or other materials in the area surrounding the enclosure. Hazardous locations may include, for example, aircraft hangars, gasoline stations, marine vessels, rigs, paint finishing locations, agricultural areas, etc.
The National Electric Code (NEC®) defines classes and divisions of hazardous locations, as well as requirements for explosion proof enclosures used in such locations. For example, a Class I hazardous location or area is one in which flammable gases or vapors are/could become present in concentrations sufficient to produce explosive and/or ignitable mixtures. Typical class I areas can include, for example, areas in marine vessels, on-shore and off-shore rigs, and petroleum processing facilities. Within Class I, a Division 1 area or location includes: one where the atmosphere of the area is expected to contain explosive mixtures of gases, vapors or liquids during normal working operations; one where ignitable concentrations frequently exist because of repair or maintenance operations; or one where there is release of ignitable concentrations of gases or vapors due to equipment breakdown, while at the same time causing electrical equipment failure. A Class I, Division 2 hazardous location includes: one where flammable liquids or gases are handled, but not expected to be in explosive concentrations, with the possibility of explosive concentrations resulting from an accidental rupture or other unexpected incident; one where ignitable gases or vapors are normally prevented from accumulating by positive mechanical ventilation, but could exist in ignitable quantities if there is a failure in the ventilation system; and areas adjacent to Class I, Division 1 locations where it is possible for ignitable concentrations of gas/vapors to enter the area due to lack of proper ventilation. Additional classes and divisions of hazardous locations are known in the art.
Explosion-proof enclosures rated for use in hazardous locations are typically equipped with one or more flame paths. Flame paths are designed for the passage and escape of burning gas resulting from an ignition that may take place within the enclosure itself (e.g., as a result of electrical arcing). As the burning gas passes through a flame path, the gas cools before being vented via the flame path into the atmosphere, thereby preventing the burning gas from igniting the volatile atmosphere in the hazardous location.
During the manufacturing and assembly of an explosion-proof enclosure, protecting the flame paths is critical to producing a safe product that conforms to regulations. A flame path located near an edge of a component of an enclosure is susceptible to being damaged when the component is handled (e.g., if the edge comes in contact with machinery or other objects) during the manufacture and assembly.
In addition, painting or otherwise coating exposed surfaces of enclosure components can lead to paint buildup at or near a flame path. Such paint accumulation can prevent access to the flame path (e.g., with a tool designed to measure the flame path to ensure it meets safe operating characteristics periodically during the lifetime of the enclosure). Furthermore, the maximum tolerance between adjacent components of explosion-proof enclosures is generally small. Paint/coating buildup on one component at or near a junction with another component can create unsafe gaps between components that exceed maximum tolerances.
There is a need for improved flame path protection and maintenance in explosion-proof enclosures.